Day1 install the JDK 8 Environment and the first java program, day1jdk 8
Install JDK 8
Step 1: Download the jdk installation package. Here we will download the jdk 8 on the orical official website.
Note: Remember to check accept when downloading.
Decompress the downloaded package:
tar zxvf jdk-8u162-linux-x64.tar.gz
Place jdk under/usr/lib/jdk8
mv jdk1.8.0_131/ /usr/lib/jdk8
Modify Environment Variables
vi ~/.bashrc
Conf jdk is our jdk8 Configuration
source ~/.bashrc
Check whether the configuration is successful
Root @ debian:/home/jeff/download # java-versionjava version "1.8.0 _ 162" Java (TM) SE Runtime Environment (build 1.8.0 _ 162-b12) Java HotSpot (TM) 64-Bit Server VM (build 25.162-b12, mixed mode)
Java boat, sailing.
The first java program
Class HelloWorld {// This is the main method, it is the program entry public static void main (String [] args) {// This is the program output System. out. print ("Hello World! "); // Print line feed with ln, and System. out. println (" Hello World! ");}}
Compile
javac hello.java
Generate the HelloWorld. class bytecode file (My defined class name is HelloWorld ).
Execution Program
jeff@debian:~/java_coding/day001$ java HelloWorld Hello World!Hello World!
There is no line feed in the output.
Java program considerations
The file name is myhello. java.
/** My first java program this is a java-specific document note * @ author jeffd * @ version 1.0 **/public class myhello {// 1. source file. end of java // 2. the source file can have classes declared by multiple classes // 3. the format of the main method (that is, the main method) in the class is fixed. // 4. main method, which is the entry of the program and the execution part of the program in the method // 5. only one public class can be declared for a source file, and the class name must be consistent with the source file name. // 6. each statement ends with a semicolon // 7. execute the program: Compile multiple projects by javac. class bytecode file, java Run // 8. multi-line comments cannot be nested with public static void main (String [] args) {// This is the output System of the program. out. print ("Hello World! "); // Print line feed with ln, and System. out. println (" Hello World! ");}}
Each program can have only one public class, and it must be the same as the file name. The javac compilation file may generate multiple bytecode files.
Java annotations
The single line comment is //.
Multi-line comment /**/. Multi-line comments cannot be nested.
Document Note :/**
@*
*/
Example:
Javadoc generates comments:
jeff@debian:~/java_coding/day001$ javadoc -d mydoc -author -version myhello.javaLoading source file myhello.java...Constructing Javadoc information...Creating destination directory: "mydoc/"Standard Doclet version 1.8.0_162Building tree for all the packages and classes...Generating mydoc/myhello.html...Generating mydoc/package-frame.html...Generating mydoc/package-summary.html...Generating mydoc/package-tree.html...Generating mydoc/constant-values.html...Building index for all the packages and classes...Generating mydoc/overview-tree.html...Generating mydoc/index-all.html...Generating mydoc/deprecated-list.html...Building index for all classes...Generating mydoc/allclasses-frame.html...Generating mydoc/allclasses-noframe.html...Generating mydoc/index.html...Generating mydoc/help-doc.html...
Generate a mudoc folder
jeff@debian:~/java_coding/day001$ lshello.java HelloWorld.class mydoc myhello.class myhello.java
jeff@debian:~/java_coding/day001$ cd mydoc/jeff@debian:~/java_coding/day001/mydoc$ lsallclasses-frame.html help-doc.html overview-tree.html package-tree.htmlallclasses-noframe.html index-all.html package-frame.html script.jsconstant-values.html index.html package-list stylesheet.cssdeprecated-list.html myhello.html package-summary.html
Open index.html to view the document style.
When the program is large enough, the document can help us better understand the usage of each class.